Embodiments of the invention relate to electronic systems, and in particular, to radio frequency (RF) electronics.
RF power amplifiers can be used to boost the power of an RF signal having a relatively low power. Thereafter, the boosted RF signal can be used for a variety of purposes, included driving the antenna of a transmitter.
Power amplifiers can be included in mobile phones to amplify an RF signal for transmission. For example, in mobile phones having a time division multiple access (TDMA) architecture, such as those found in Global System for Mobile Communications (GSM), code division multiple access (CDMA), and wideband code division multiple access (W-CDMA) systems, a power amplifier can be used to amplify an RF signal. It can be important to manage the amplification of an RF signal, as a desired transmit power level can depend on how far the user is away from a base station and/or the mobile environment. Power amplifiers can also be employed to aid in regulating the power level of the RF signal over time, so as to prevent signal interference from transmission during an assigned receive time slot.
IEEE 802.11af is a wireless networking standard in the 802.11 family that allows wireless local area network (WLAN) operation in TV white space spectrum. For IEEE Standard 802.11af, a power amplifier to boost the transmitted WiFi signal is used in the band frequencies between approximately 470 MHz to approximately 928 MHz (full band). In a less-than-perfectly linear amplifier, harmonics of the signals at 470 MHz manifest at 940 MHz, which is perilously close to the end of the full band at 928 MHz. In other words, harmonics of the lower frequencies of the full band will be amplified and passed on to the next element in the radio frequency (RF) signal chain unless they are rejected without impacting the operation of the amplifier at the higher frequencies of the full band. Moreover, RF signals below approximately 470 MHz may unintentionally be present in the input RF signal and consequently rejection of harmonics of those signals is needed when operating the amplifier at the lower end of the band.
For efficient, broadband operation of a power amplifier, the output matching network (OMN) of the amplifier should be optimized for all frequencies within the frequency band of operation. However, rejection of harmonic frequencies from the lower part of a wide frequency band is a challenge because the OMN is optimized to match the amplifier at those harmonic frequencies as well, rather than reject them (i.e. twice the frequency of the lower band of frequencies is within the range of the higher band of frequencies).
There is a need for improved broadband power amplifiers. Furthermore, there is a need for improved power amplifier matching networks.